Freeke van de Voort (Cardiff University)

To understand the distribution of rapid neutron capture (r-process) elements, we have to understand the complexity of galaxy formation, including gaseous inflows and outflows and galaxy mergers. We therefore ran a suite of cosmological, magnetohydrodynamical simulations of a Milky Way-mass galaxy with a variety of models for the sources of r-process elements. In this talk, I will focus on neutron star mergers as the dominant source and the effect of neutron star natal kicks on the r-process abundances of stars across the metallicity range. The kicks are, for the first time, included on-the-fly in the simulations. With kicks, neutron star mergers are more likely to occur outside the galaxy disc, but how far the binaries travel before merging also depends on the kick velocity distribution and shape of the delay time distribution for neutron star mergers. The resulting scatter in r-process abundances is much larger with natal kicks, especially at low metallicity, giving rise to more r-process enhanced stars. I will compare our results to observational data and discuss whether or not neutron star mergers can be the only source of r-process elements in the universe. I will argue that it is possible that that the observed scatter in r-process abundances is predominantly caused by natal kicks rather than the usual interpretation that the scatter is set by the rarity of its production source.